Mexican Tetra (Astyanax mexicanus)

Distribution: Originally found in the Nueces River, the lower Rio Grande and lower Pecos River drainages in Texas as well as eastern and central Mexico. They are now found elsewhere in Texas (mostly streams on the Edwards Plateau) and New Mexico (throughout the Pecos River system) and disjoint locales in Oklahoma, Louisiana and Arizona.
Length: 4"
Water Temperature: 68 to 77 degrees Fahrenheit (20-25 degrees Celsius)
Diet: They eat small live foods in the wild. They'll greedily eat those in the aquarium, but won't shy away from eating quite a bit of high-quality prepared foods there.
Water Chemistry: Moderately hard conditions are best; harder is okay, but acclimation may be needed.
pH: 7-8.5 recommended
Lifespan: 5 years

Species Description These are small laterally-compressed fish replete with a a rounded ventral surface and a rounded, bullet tip-shaped snout. They are either mostly white in coloration with a somewhat silvery sheen or pale brassy in coloration. They are silver to olive in ventral coloration. They have a diamond shape black mark at the caudal peduncle which extends above the lateral line to behind the eyes and back to the caudal fin notch as a black bar.

These fish have an adipose fin. For the males, all fins are colorless except for the pectoral, anal and very bifurcated caudal. The pectorals are somewhat pink and the caudal is yellowish-gold with the aforementioned black band. The anals are somewhat pink to red with black edging. Southern forms have less red and more yellow in the anal and pectoral fins.

Females have similar fin coloration, but it is absent on the pectoral fins and much less intense on all others.

Species Behaviour These are lively schoolers which "[resemble] shiners in behavior". They have reputations as both plant-eaters and fin-nippers but are generally peaceful when their boisterousness is discounted.

Natural Conditions Pools with rocky and sandy substrata, backwaters of creeks and rivers as well as springs.

Natural Range Originally found in the Nueces River, the lower Rio Grande and lower Pecos River drainages in Texas as well as eastern and central Mexico. They are now found elsewhere in Texas (mostly streams on the Edwards Plateau) and New Mexico (throughout the Pecos River system) and disjoint locales in Oklahoma, Louisiana and Arizona.

Water Quality Moderately hard, neutral to somewhat alkaline conditions are best. Harder conditions are okay, but acclimation may be needed.

Sexing Females are larger and have more girth but less intensity of color in their fins.

Breeding The sexes should be separated for a conditioning period of two to four weeks, during which time they receive extremely clean water and plenty of live foods. Though this isn't necessary, it pays off in spades. Once conditioned separately, a pair or trio of two males and one female can be placed together in a tank of at least ten gallons for a pair, fifteen to twenty for the trio. Lengthy photoperiods are helpful; 24 hours was suggested in the www.nativefish.org article. Many hiding places should be provided so that the female can hide from her boisterous suitors.

The spawning event is much like that of other egg-scatterers. Unlike the majority of widely-kept egg-scatterers, well-conditioned parents are not avid oophages. After two days, they are done and may be removed for reconditioning for another bout.

These eggs are somewhat adhesive, soft and fragile. Dislodging them from their position may cause irreparable damage. Though they do not seem to be sensitive to light, exposure to strong sunlight is contraindicated.

At 75 degrees Fahrenheit (24 degrees Celsius, the eggs hatch in about 24 hours. (At the cool end of the successful spawning range, the eggs may take up to three days to hatch.) After about three days, the fry are able to accept the smallest of rearing foods (perhaps infusoria or green water). In a few more days, they are ready for brine shrimp nauplii.

They reach sexual maturity after about six months.

Feeding They eat small live foods in the wild. They'll greedily eat those in the aquarium, but won't shy away from eating quite a bit of high-quality prepared foods there.